Switching Dynamics of Thin Film Ferroelectric Devices

Colloquium: Departmental | December 2 | 3:10-4 p.m. | 540AB Cory Hall

 Khalid Ashraf

 Electrical Engineering and Computer Sciences (EECS)

In this talk, we describe our efforts to reduce the gap between computational device design and their experimental realization incorporating strongly correlated materials. Strongly correlated materials like ferroelectrics and ferromagnets offer alternative state variables for computation that are robust against thermal excitation. In some materials, these states coexist and are strongly coupled, facilitating manipulation of one by controlling the other. Thus these materials are of inherent interest for low power and multi-functional devices. However, possible device applications of these materials have been limited due to the poorly understood electromagnetic and mechanical response at the nanoscale in arbitrary device structures.

The difficulty in understanding switching dynamics mainly arises from the presence of features at multiple length scales and the nonlinearity associated with the strongly coupled states. For example, in a ferroelectric material, the domain walls are of nm size whereas the domain pattern forms at micron scale. The switching is determined by coupled chemical, electrostatic, mechanical and thermal interactions. Thus computational understanding of switching dynamics in thin film ferroelectrics and a direct comparison with experiment poses a significant numerical challenge.

We have developed a phase field model that describes the physics of polarization dynamics at the microscopic scale. A number of efficient numerical methods have been applied for achieving massive parallelization of all the calculation steps. Conformally mapped elements, node wise assembly and prevention of dynamic loading minimized the communication between processors and increased the parallelization efficiency. With these improvements, we have reached the experimental scale - a significant step forward compared to the state of the art thin film ferroelectric switching dynamics models.

We will describe the physics of ferroelectric switching, outline the difficulty in understanding the process, review the current state of the art in phase field description of switching dynamics. Then we will present the key improvements offered by our model and show some specific device applications where the model has been useful in elucidating the physics of polarization domain switching. We will end with some open questions and areas where the model could be useful.